Tire pressure sensor device

ABSTRACT

A tire pressure sensor device ( 122 ) for a wheel ( 112 ) of an aircraft ( 102 ) including a pressure sensor ( 124 ) for measuring the internal pressure of a tire, a temperature sensor ( 126 ) for measuring a temperature local to the tire ( 116 ), a memory unit ( 131 ) local to the tire for storing data, and a control unit ( 128 ) local to the tire arranged to record in the memory unit ( 131 ) data of the readings taken at intervals of time. The data recorded for each reading includes an indication of the time of the reading, the tire pressure and the temperature local to the tire. Measurements may be taken and recorded over time, both when the aircraft is on the ground and when the aircraft is in flight. Data may be uploaded to a portable handheld device ( 140 ) for analysis when maintaining the tires in their correctly inflated state.

RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.16/232,587 (now U.S. Pat. No. 10,875,366) filed Dec. 26, 2018, which isa continuation of U.S. patent application Ser. No. 15/212,085 (now U.S.Pat. No. 10,183,534), filed Jul. 15, 2016, which claims priority toGreat Britain patent application GB 1512488.6 filed Jul. 16, 2015, theentirety of each of these applications is incorporated by reference.

BACKGROUND OF INVENTION

The present invention concerns a tire pressure sensor device, forexample for an aircraft. More particularly, but not exclusively, thisinvention concerns a tire pressure sensor device and a method ofmonitoring the pressure of a tire on an aircraft. The invention alsoconcerns an aircraft including multiple such tire pressure sensordevices, and a kit of parts including such a tire pressure sensordevice.

Some modern aircraft, with landing gear assemblies, are equipped with anintegrated tire pressure indicating system. Such a tire pressureindicating system includes tire pressure sensors which take tirepressure measurements which are displayed in a cockpit of the aircraft.

An integrated aircraft tire pressure monitoring system is disclosed inUS-A-2008/0055060. A sensor senses an operating parameter of the tire(such as pressure or temperature), and a signal related to the sensedparameter is transmitted to a reader located on or in an aircraftfuselage. The reader may also transmit some or all of the information toanother device, such as a display.

Despite the advent of integrated aircraft tire pressure monitoringsystems, there are still ways in which tire pressure indicating could beimproved.

Such integrated tire pressure indicating systems do not make it easy forground crew to check tire pressure of an aircraft when performing tirepressure checks, as they are then required to board the aircraft andaccess the tire pressure indicating system, which may not be a trivialtask.

Some aircraft do not include any integrated tire pressure measuring andindicating systems. Retro-fitting such a system is an expensive andtime-consuming process.

Alternatively, tire pressures may be check manually on a tire by tirebasis by means of manually attaching and using a portable pressure gaugedevice. Such manual checks may also be the subject of improvement.

With manual tire pressure checks, it may be difficult to make andmaintain a reliable record of aircraft tire pressures. The conditions atwhich tire pressures are manually taken may vary. The intervals betweenthe recording of reliable tire pressure measurements may at best be onceevery flight, and may in certain circumstances be less frequent. Thus,whilst tire pressures may be readily checked manually, the systematicrecordal of such measurements may be difficult to implement and manage.

The present invention seeks to mitigate one or more of theabove-mentioned problems. Alternatively or additionally, the presentinvention seeks to provide an improved tire pressure sensing device foran aircraft.

SUMMARY OF THE INVENTION

The inventor has conceived of and discloses here a tire pressure sensordevice including a pressure sensor for measuring the internal pressureof a tire. The tire may, for example, be on an aircraft wheel. Thedevice includes a locally positioned control unit arranged to record ina memory unit data in respect of multiple pressure readings over time.The control unit may be locally positioned relative to the pressuresensor. It may be that the control unit is, in use, positioned local tothe tire. Both pressure sensor and control unit may form part of, or belocal to, the same single device. The data recorded by the control unitin the memory unit for each such reading includes an indication of thetime of the pressure reading and the pressure as measured by thepressure sensor for that pressure reading. The memory unit may also bepositioned locally.

The tire pressure sensor device may also include a temperature sensor.The readings may thus include an indication of the temperature asmeasured by the temperature sensor. The temperature sensor may also bepositioned locally. The temperature measured by the temperature sensormay be the temperature local to the tire. It is preferred that thetemperature measured is indicative of the temperature of the gas in thetire. It may be that an additional or alternative temperature sensor isprovided for measuring ambient temperature. The temperature sensor maybe carried by the wheel on which the tire is mounted. The temperaturereadings may be taken at the same time as their associated pressurereadings, or shortly before or after their associated pressure readings.

Thus, in accordance with certain embodiments of the invention, there isprovided a single pressure sensing device for monitoring the pressure ofan aircraft tire, wherein all operative parts of the device are (when inuse) mounted locally to the aircraft tire, and wherein the device isconfigured to take and record multiple successive measurements, spacedout over a period of time (of a number of hours or days), of bothpressure and temperature of the tire for subsequent analysis. Such adevice can be used in relation to an aircraft that is not equipped withan integrated tire pressure monitoring system. More data can becollected than manual pressure monitoring methods can provide. Data canbe acquired and recorded in a more systematic and verifiable manner thanmanual pressure monitoring methods can provide.

The tire pressure sensor device may include a communication modulefacilitating communication with a separate electronic device. Theseparate electronic device may be provided external to the aircraft. Theseparate electronic device may be a reader device. The communicationbetween the pressure sensor device and the separate electronic devicemay be wireless communication, preferably secure wireless communication,for example utilising encryption of some form. The memory unit mayinclude security key data facilitating such secure communication. Theseparate electronic device may be a portable device, possibly ahand-held device.

The use of a hand-held device to wirelessly obtain pressure readings, asprovided in certain embodiments, allows a single ground crew member tocheck quickly a large number of aircraft tires without having to enter acockpit or check the pressure of each tire manually. This may be ofparticular benefit in the case where the associated aircraft has noother on-board automated tire pressure indicating system.

It may be that the tire pressure sensor device includes a motion sensor.The motion sensor may be arranged to detect motion of an object from oneposition to another simply by means of detecting whether the object isin a given position or not. Such a motion sensor may thus merely providea binary output. The motion sensor may be configured to indicate whetherthe landing gear assembly of the wheel on which the tire is mounted isdeployed or stowed away. The motion sensor may be in the form of a tiltdetector, which may for example be configured to indicate whether thelanding gear assembly of the wheel on which the tire is mounted isdeployed or stowed away. The motion sensor may be configured to detectspeed of rotation of the wheel. The motion sensor may be in the form ofan accelerometer, which may for example be configured to detect speed ofrotation of the wheel. There may be more than one motion sensorassociated with the device. There may for example be both a tiltdetector and an accelerometer. The control unit may be arranged todetect, for example with the use of one or more motion sensors, at leastone of (a) whether the aircraft is in flight and (b) whether theaircraft is on the ground. The control unit may be provided with amotion sensor which detects when the landing gear is stowed in whichcase it can be sure that the aircraft is in flight. When such a motionsensor detects that the landing gear is deployed it may not withoutother information be able to determine whether the aircraft is in flightor on the ground. Similarly, the control unit may be provided with amotion sensor which measures the speed of rotation of the wheel. Themeasure merely of the speed of rotation of the wheel will not besufficient to determine whether the aircraft is in flight. Pastmeasurements may also be needed to determine with confidence whether theaircraft is in flight or on the ground. Having a device which can itselfascertain whether or not the aircraft is on the ground or in flight isimportant because firstly the pressure readings for tires are higher inthe weight-on-wheels condition, than when in flight, and secondlybecause requiring information to be ascertained from other systems onthe aircraft would add complication. There may be benefits in the tirepressure sensor device being one that relies very little, if at all, onother systems already integrated on certain aircraft. The or each motionsensor may be provided locally, for example within a housing of thedevice.

It may be that the control unit is configured to record in memory bothdata relating to a reading taken when the aircraft is on the ground anddata relating to a reading taken when the aircraft is in flight. It ispreferred that the taking of at least certain readings by the controlunit of tire pressure is dependent on the control unit ascertaining thatthe aircraft has landed or is dependent on the control unit ascertainingthat the aircraft has taken-off. There may be a set delay (for exampleof at least ten minutes) between so ascertaining take-off or landing,and taking the measurements.

It may be that the data recorded for each such reading includes anindication of whether the aircraft is on the ground. It may be that anabsence of an indication of the aircraft being on the ground can beassumed to be an indication that the aircraft is flying (but notnecessarily). It may be that the data recorded for each such readingincludes an indication of whether the aircraft is in flight. It may bethat an absence of an indication of the aircraft being in flight can beassumed to be an indication that the aircraft is on the ground (but notnecessarily). It may be that the data recorded for each such readingincludes an indication of whether the aircraft is on the ground or inflight, as a binary value (“on ground” or “in flight” and no otherpossibility such as “not known”)

It may be that the control unit is so arranged that it is effectivelyprevented from recording a reading for which it is not known withconfidence whether the aircraft is in flight or on the ground. Thecontrol unit may for example be arranged such that, immediately aftertake-off, when the landing gear is still deployed and the wheels arestill spinning that the control unit cannot tell with certainty whatstate the aircraft is in (on-ground or in-flight). There may be apre-set time delay or other criteria for ensuring that the control unitis prevented from recording a reading without knowing whether theaircraft is in flight or on the ground. The control unit can infer sucha state by monitoring wheel speed, detecting deployment or stowage oflanding gear, and from historical measurements.

The memory unit may include an indication of a reference tire pressurefor the tire. Such a reference tire pressure may be used to ascertainwhether and when the tire is under-inflated. The memory unit may includevarious other data, including for example a code identifying theaircraft, or other metadata. Proving details of the aircraft ID orassociated reference pressure levels may enable the ground crew memberto quickly and reliably check the tire pressures of a fleet containingdifferent aircraft types, using the aforementioned separate electronicdevice (for example a handheld device). When such a handheld devicedownloads data from the memory of the sensor device, the handheld unitmay be arranged to compare the reference pressure with the actualpressure and to indicate whether the actual pressure (or the trend inpressure reduction over time) is suggestive that the tire is, or soonwill be, underinflated. In such a case the separate electronic devicemay be configured to show a warning message.

The tire pressure sensor device is may be self-contained. Whilst partsat least of the pressure and temperature sensors may need to be providedoutside the main body of the device, it is preferred that the device hasa housing which accommodates the input ports for receiving measurementsfrom the pressure sensor and the temperature sensor. At least a part ofthe pressure sensor (for example an input port) may thus be providedinside the housing. At least a part of the temperature sensor (forexample an input port) may thus be provided inside the housing. Such ahousing would for example also accommodate the control unit and thememory unit. The device may include a local source of electric power,for example a battery-based power source. The device may weigh less than500 g, preferably less than 200 g. The mass may be sufficiently low thatits presence off-axis on the wheel presents no significant wheelbalancing issues, in view of the total mass of the wheel including thetire. The housing may have a maximum dimension of less than 200 mm. Itmay be that the housing has a maximum dimension less than 100 mm.

The tire pressure sensor device may be provided on or in respect of anaircraft wheel. There is thus provided a tire pressure sensor deviceprovided on an aircraft wheel, the device being in accordance with anyaspect of the present invention as claimed or described herein,including any optional features relating thereto. It is preferred thatthe device is largely self-contained. All parts of the device maycarried by the wheel (and may be specifically arranged and configuredwith that in mind). Some parts of the device may be positioned insidethe tire. Some parts of the device may be provided on adjacent structuresuch as a wheel axle. In the case where a motion sensor detects that thelanding gear is deployed or stowed, the motion sensor may be mounted onanother part of the landing gear. There may be wireless communicationbetween parts of the device to allow for some parts to be separated from(but still local to) the main housing of the device. There may bewireless communication between a sensor within the tire and the rest ofthe device which is mounted outside the tire. There may for example bewireless communication between a sensor within the tire and an inputport (for receiving a measurement from the sensor) associated with therest of the device which is mounted outside the tire. The invention alsoprovides an aircraft wheel, or a landing gear assembly comprising such awheel, which is provided with a tire pressure sensor device inaccordance with any aspect of the present invention as claimed ordescribed herein.

The tire pressure sensor device may include attachment means forattaching the device to the wheel body. The attachment means maycomprise one or more parts that are arranged to engage with a recess inthe wheel specifically provided for a pressure sensing device. Theattachment means may be in the form of nuts and bolts. The attachmentmeans may comprise a strap. The attachment means may facilitate clippingthe device to the wheel. The attachment means may facilitate clampingthe device to the wheel. The attachment means may include a threadedpart that mates with a corresponding threaded part on (whetherseparately attached or not) the wheel. The threaded part may providefluid communication to allow for sensing of the internal pressure. Theremay be a holder unit connected to the wheel, wherein the holder unit isconfigured to receive and accommodate the device. The holder unit mayprovide an interface, for example including a valve, between the deviceand the wheel. The holder unit may be an integrated part of the wheel.The holder unit may be removably connected to the wheel. The device maybe removably attached to the wheel body via a valve that provides forfluid communication to allow for sensing of the internal pressure. Theremay be a separate valve integrated with the wheel allowing for inflationor deflation of the tire.

One embodiment of the invention concerns a tire pressure sensor devicefor a wheel of an aircraft including (a) a pressure sensor for measuringthe internal pressure of a tire, (b) a temperature sensor for measuringa temperature local to the tire, (c) a memory unit local to the tire forstoring data, and (d) a control unit local to the tire arranged torecord in the memory unit data in respect of multiple readings overtime, the data so recorded for each such reading including an indicationof the time of the reading, the pressure as measured by the pressuresensor and the temperature as measured by the temperature sensor.

The present invention may be embodied, according to a second aspect, asan aircraft including multiple tire pressure sensor devices. Each suchtire pressure sensor device may be associated with a differentrespective wheel of the aircraft. Each tire pressure sensor device maybe in accordance with any aspect of the present invention as claimed ordescribed herein, including any optional features relating thereto.

Data from multiple sensors, particular when captured in a coordinatedmanner, can provide extra benefits. For example, reliable data onwhether a landing gear assembly is stowed or deployed may not beavailable on all landing gear assemblies (there may be no tilt switchprovided for example), but other sensor devices may include reliableindications of when the landing gear switches between the stowed anddeployed positions. In such a case such reliable indications of whetherthe landing gear is stowed or deployed at certain times of measuringtire pressure may be utilised in respect of the data from the sensorsnot including such reliable data.

There is also provided a kit of parts including a tire pressure sensordevice according to any aspect of the present invention as claimed ordescribed herein, including any optional features relating thereto. Thekit may comprise a portable reader device, which may for example beconfigured for use externally of the aircraft. The tire pressure sensordevice and the portable reader device are both configured forfacilitating electronic communication, preferably wirelessly, betweeneach other. There may be multiple such tire pressure sensor devices inthe kit.

The invention may also be embodied as a method of monitoring thepressure of a tire on an aircraft, particularly (i.e. but notnecessarily) using a pressure sensing device according to any aspect ofthe present invention as claimed or described herein, including anyoptional features relating thereto. There may be a step of a controlunit causing first measurements to be taken of the tire pressure and,optionally, of an associated temperature. There may be a step of thecontrol unit recording in a memory unit first data including anindication of the time at which the first measurements are taken, anindication of the tire pressure and, optionally, an indication of thetemperature as so measured by the first measurements. There may be astep of the control unit causing second measurements to be taken of thetire pressure and, optionally of an associated temperature. There may bea step of the control unit recording in the memory unit second dataincluding an indication of the time at which the second measurements aretaken and an indication of the tire pressure and optionally anindication of the temperature as so measured by the second measurements.It may be that the method is so performed that one of the first andsecond measurements is taken when the aircraft is on the ground and theother of the first and second measurements is taken when the aircraft isin flight. It may be that the time between the first and secondmeasurements being taken is longer than one minute, preferably more than10 minutes. It may be that the time between the first and secondmeasurements being taken is less than twenty-four hours, preferably lessthan 7.5 hours.

Optionally the in-flight pressure reading is normalised to take accountfor the tire being unloaded. Optionally, one or more pressure readingsmay be normalised to take account of temperature. Such normalisation maybe carried out by the control unit, but it may be preferred in someembodiments for a separate computer device to perform such dataprocessing tasks.

It may be that multiple successive sets of measurements are taken andcorresponding multiple successive sets of data are recorded in thememory unit. The interval between successive measurements may be between10 minutes and 7.5 hours (7.5 hours being approximately the averageflight time for Airbus' A380 aircraft). The interval between successivemeasurements when the aircraft is in flight may be more than 1 hour. Atleast one set, and preferably at least two sets, of measurements aretaken when the aircraft is in flight,

More than three, and preferably more than ten, successive sets ofmeasurements are taken and stored in the memory of the device. The datarecording may thus span several flights.

The method may be performed over a period of time of one or more days.Data may be recorded on a rolling basis, such that data older than acertain time are overwritten with new data. There may for example be atleast 72 hours of rolling data, and preferably at least 120 hours. Itmay during performance of the method there are a set number of data setsstored in memory, the set number being greater than 25 (optionallygreater than 50) but fewer than 1,000, and possibly fewer than 250. Itmay be that as a new set of data is stored, the oldest set of data isdeleted (effectively overwritten).

It may be that one of the first and second measurements is triggered bydetection of a change in the speed of spinning, if any, of the tire. Itmay be that one of the first and second measurements is triggered bydetection of the speed of spinning of the tire passing a thresholdamount (for example falling from a higher amount via the thresholdamount to a lower amount). It may be that one of the first and secondmeasurements is taken after a set time delay dependent on the detectionof the change in the speed of spinning The set time delay may forexample be a set time after the start of tire spinning is detected. Theset time delay may for example be a set time after it has beenascertained that the tire has stopped spinning

The method may include a step of wirelessly sending stored data from thecontrol unit of the device to a handheld device, for example theabove-mentioned portable reader device or other separate electronicdevice. The same handheld device may be used to download data frommultiple tire pressure sensor devices of the invention on an aircraft,preferably all of the multiple tire pressure sensor devices. The samehandheld device may be used to download data from multiple tire pressuresensor devices substantially (from the user perspective, for example)contemporaneously. The range of communication is preferable at least 10metres and may be more than 100 m. The same handheld device may be usedto download data from multiple tire pressure sensor devices of theinvention on multiple aircrafts.

The method may include a step of deciding whether or not to add more gasto the tire (e.g. to further inflate the tire), the decision dependingon data received by a separate electronic device, for example theabove-mentioned portable reader device. The decision may be taken by theseparate electronic device and be provided as an output, for example viaa visual display unit of the separate electronic device. The decisionmay be taken taking into account one or more historical measurements, inaddition to a more recent measurement (for example the last measurementtaken before making the decision). The method may then include a step ofinflating the tire, if so directed by the separate electronic device.

The method may include a step of deciding whether or not to replace thetire, the decision depending on data received by a separate electronicdevice, for example the above-mentioned portable reader device. Thedecision may be taken by the separate electronic device and be providedas an output, for example via a visual display unit of the separateelectronic device. The decision may be taken taking into account one ormore historical measurements, in addition to a more recent measurement(for example the last measurement taken before making the decision). Theseparate electronic device may for example detect that the tire pressurein the tire had reduced more rapidly than would be expected of a tire ingood health. The method may include a step of replacing the tire, if sodirected by the separate electronic device.

There may be a step of uploading data from the separate electronicdevice, which will typically be a portable device, to a furthercomputer, for example a central server, so that data can be collated.Such collated data may then be used for fleet-wide analytics orarchived.

When collating data from multiple tire pressure sensor devices, the datafrom one or more devices may be used in relation to assessing the datafrom one or more other devices. For example, some devices may detectwith greater accuracy whether the aircraft is on the ground or not, theresulting information from which can be used to normalise pressurereadings on other devices. It is preferred that all devices are of thesame design, but that need not be the case. For example, differentdevices could be used on the main landing gear (MLG) from the noselanding gear (NLG). Not all devices need be provided with functioningmotion sensors, for example.

It will of course be appreciated that features described in relation toone aspect of the present invention may be incorporated into otheraspects of the present invention. For example, the method of theinvention may incorporate any of the features described with referenceto the apparatus of the invention and vice versa.

DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described by way ofexample only with reference to the accompanying schematic drawings ofwhich:

FIG. 1 shows an aircraft according to a first embodiment of theinvention;

FIG. 2 shows a landing gear assembly of the aircraft of FIG. 1 showingtwo tires to which are attached two smart sensor devices of the firstembodiment of the invention;

FIG. 3 shows schematically the function of the first embodiment of theinvention;

FIG. 4 is a flow chart illustrating an example method of tire pressuremonitoring in accordance with a second embodiment of the invention; and

FIG. 5 is a graph (not to scale) showing the timing of tire pressuremeasurements in an example method of the second embodiment of theinvention.

DETAILED DESCRIPTION

FIG. 1 shows an aircraft 102 comprising a pair of wings 104 and afuselage 106. The wings each carry an engine. The aircraft 102 issupported on the ground by sets of landing gear assemblies comprising amain landing gear (MLG) 108 and a nose landing gear (NLG) 110. Thelanding gear assemblies comprise wheels 112 which are shown in FIG. 1 incontact with the ground (e.g. runway). The landing gear assemblies aremounted for movement between a deployed position in which the main strutof each landing gear is generally vertical and a stowed position inwhich the strut is generally horizontal. The MLG 108 is shown in greaterdetail in FIG. 2 together with a schematic illustration of the wheels112. Parts of the landing gear 108 including, for example, the axles formounting the wheels and the upper part of the landing gear assembly,have been omitted from FIG. 2 for the sake of clarity. Each wheel 112comprises a rim 114 on which there is mounted a tire 116. The hub of thewheel is covered by means of a hub cover 118 (which may also function asa brake cooling fan guard, in the case where such fans are provided). Onthe main body 120 of each wheel 112, there is mounted a smart sensordevice 122, which rotates with the wheel.

The wheel body has a port (not shown) which is configured for attachmentof a pressure sensor holder, which both releasably holds the device 122in place, and also allows the device to be attached or removed withoutloss of tire gas pressure. (In other embodiments the smart sensor devicemay be fixed to the wheel body by means of a different form ofattachment or may be fixed to the wheel body directly, for example byhaving a threaded part which interfaces with a corresponding mating porton the wheel). There may be many wheels, each with a tire and associatedsmart sensor device 122, on the aircraft.

Each smart sensor device 122 has a mass of about 120 g, is generallycylindrical in shape with a diameter of about 30 mm and a length ofabout 90 mm.

The smart sensor device 122 is shown schematically in FIG. 3. The deviceincludes a tire pressure sensor 124, which is contained within thedevice 122 and measures the pressure in the tire via the gas port of thewheel body to which the pressure sensor holder is connected. (In analternative embodiment, the pressure sensor is located within the tireand connects wirelessly to the device 122.) The device also includes atire temperature sensor 126 for measuring the temperature of thesensor-wheel interface, from which temperature the tire gas temperaturemay be derived. (In an alternative embodiment, the temperature sensor islocated within the tire and connects wirelessly to the device 122.) Thesmart sensor device 122 also includes a processor (CPU 128) with aninternal clock 130 and an associated memory 131.

The device 122 also includes an accelerometer 132 which can be used toascertain the angular speed of wheel rotation and a tilt switch 134which can be used to detect when the landing gear is moved between thedeployed position and the stowed position. The processing unit 128 isintegrated with a communications module 136 which, via an antenna 138,provides for wireless communication with a handheld device 140. Thesensor device 122 has its own rechargeable power supply (not shown).

Each of the smart sensor devices 122 has a unique ID no. associated withit, which is stored in the memory unit 131. Also stored in the memoryunit are data including the aircraft's ID number, security key datawhich facilitates secure encrypted wireless communication with theseparate handheld device 140, and an indication of the expected tirepressure at a given temperature (a “reference pressure”). Othermeta-data may be stored in the memory unit 131.

Operation of multiple smart pressure sensor devices on an aircraft willnow be described with reference a second embodiment of the invention.The smart sensor devices may each be in the form of a device asdescribed above in relation to the first embodiment. All of the smartsensor devices on the aircraft operate in the same way. Operation of oneof the sensor devices will now be described with reference to FIG. 4,which shows a method, according to the second embodiment, of operationof a smart pressure sensor device before take-off and an end time aftersubsequent landing. The sensors once installed are always powered “on”but for the sake of the present description the process will bedescribed from an arbitrary start time 202. Thus, initially the sensortakes (step 204) an initial set of readings and stores them (step 206)in memory as a first reading. The data stored includes the time of themeasurement, an indication of the temperature measured, an indication ofthe pressure measured, and an indication of the whether the aircraft ison the ground or in flight according to the control unit. Optionally,the tilt switch position is included in the data so recorded. For thefirst set of data recorded it is assumed that the aircraft is on theground. The fact that a landing gear assembly is deployed can beverified by the control unit of the smart sensor by means of the outputfrom the tilt switch. The device monitors (step 208) for wheel movementby monitoring the output from the accelerometer. Once the wheel hasstarted spinning (indicated by branch labelled “yes”), the control unitmonitors wheel speed (as derived from the readings of the accelerometer)to detect when take-off has completed. After take-off, the wheels willstop spinning, if for no other reason through friction. The control unitnotes the time at which the wheel stops spinning, and then waits (step210) for 30 minutes, at which point (i.e. 30 minutes after the wheel hasstopped spinning) the tire pressure and temperature are measured (step212 and the corresponding data set recorded again (step 214). Withreference to FIG. 4 if, after a wait time of 3 hours (see referencenumeral 209) from the start 202 of the process, no wheel movement isdetected (indicated by branch labelled “no”), the device will perform anew set of measurements (box 204) and record a new set of data (box206), and continue doing this until such time as wheel movement isdetected. 30 minutes after the wheel has stopped spinning, it is assumedthat the aircraft is in flight. It is likely that the landing gearassembly is stowed at this time (at least 30 minutes after take-off)and, if so, that can be verified by the control unit of the smart sensorby means of the output from the tilt switch. The reason for measuringpressure and temperature at least 30 minutes after take-off is that itis assumed that the tire will by then have returned to its steady statecondition, with the temperature sensor thus accurately representing thetemperature of the gas within the tire. By this time, the control unithas recorded two sets of data, one on the ground before take-off and oneshortly after 30 minutes after take-off.

The control unit then records further measurements at three hourlyintervals until the device detects the wheel spinning again. Thus, ifthree hours elapse (arrow 216) since the last reading without detectingspinning of the wheel (box 218), the control unit assumes that theaircraft is still in flight and takes a further set of measurements(step 220) and records (step 222) the ith set of data (where i is thenumber of the data set so recorded). This process is repeated (box 224)every 3 hours, until the control unit detects (step 226) rotation of thewheel as indicated by means of the output from the accelerometer. Atthis point it is assumed by the control unit that the aircraft hastouched down. After the control unit has detected the spinning up of thewheel on landing (as indicated by arrow 225), the control unit monitorswheel speed (as derived from the readings of the accelerometer) todetect when landing has completed. When the aircraft has come to a rest,the control unit waits (step 228) for 30 minutes, and then measures(step 230) the tire pressure and temperature and the corresponding dataset are then recorded (step 232). By this time it is hoped that thebrakes will have cooled sufficiently not to significantly affect thepressure and temperature readings.

Further readings are then taken at 3 hourly intervals, and the processtherefore continues (as signified by arrow 234). The data sets stored inmemory are recorded on a rolling basis so that the memory unit requiredfor storing the data can be relatively small and simple. There issufficient memory for 70 sets of data, which (depending on the number ofseparate flights during a given period) will be sufficient for of theorder of 7 days' worth of data.

It will be seen that for a 7 hour flight, there will be a first readingon the ground, a second reading 30 minutes after take-off, third andfourth readings in flight, and then a final and fifth reading 30 minutesafter coming to a stop after landing. The readings having beensystematically taken, and recorded, for all tires at various set times,both on the ground and at regular intervals during flight providesbetter and richer data than could be provided by means of manuallymeasuring and recording tire pressures on the ground before and afterflight. Trends in tire pressure of one or more tires can be monitored.Differences between tire pressures of tires that are in very similar,steady-state, conditions (when in flight) can be more readilyidentified.

Data recorded over several flights may be recorded on the memory unit.Data is wirelessly downloaded from the sensor by means of a handhelddevice 140 (i.e. not on the aircraft) when the aircraft is on theground. One device may be able to download data from many sensors atsubstantially the same time, without needing to walk round to eachwheel. Such data can then be used to monitor tire pressures over time inan accurate and controlled manner, without the need of an on-aircrafttire pressure monitoring system such as TPIS (“Tire Pressure IndicatingSystem”). The control unit 128 monitors periodically for a request, fromsuch a device 140, for a data upload to the device 140. Communicationbetween the control unit 128 and the device 140 is encrypted usingstandard encryption techniques. Security key data is held on the controlunit 128 for this purpose. When such a handheld device downloads datafrom the memory of the smart sensor device, the handheld unit comparesthe reference pressure with the actual pressure and if the actualpressure (or the trend in pressure reduction over time) is suggestivethat the tire is, or soon will be, underinflated a warning message willappear. The tire may then be inflated manually. The handheld unit mayalso be able, by analysing the historical pressure measurements,recommend replacing a tire or provide an indication of the health of thetire. The tire may be replaced on recommendation of the handheld unit.

FIG. 5 is a graph showing the times at which measurements are made whenperforming the method of the second embodiment, using the example of twosuccessive flights. The vertical axis represents wheel speed, s_(w). Thehorizontal axis represents time, t. The graph is not to scale and partsof the graph have been exaggerated and shifted to illustrate the variousstages of operation (for example the vertical position on the graphrepresenting the speed of the wheels when not rotating has been shiftedupwards from the horizontal axis). A first set of readings are taken(time 301) with the aircraft stationary on the ground (region 320).After 3 hours (“3 h”) a second set of readings are taken (time 302).Then wheel movement is detected, suggesting taxiing and take-off (region321). 30 minutes (“½ h”) after the wheels stop moving, a third set ofreadings are taken (time 303) with the aircraft in flight (region 322).Then wheel movement is detected, suggesting landing and taxiing (region323). 30 minutes after the wheels stop moving, a fourth set of readingsare taken (time 304) with the aircraft stationary on the ground (region324). 3 hours and 6 hours later, fifth and sixth sets of readings aretaken (times 305 and 306, respectively), with the aircraft remainingstationary on the ground. Then wheel movement is detected again,suggesting taxiing and take-off again (region 325). 30 minutes after thewheels stop moving, a seventh set of readings are taken (time 307) withthe aircraft in flight (region 326). 3 hours, 6 hours and 9 hours later,eighth, ninth and tenth sets of readings are taken (times 308, 309 and310, respectively) with the aircraft in flight. Then wheel movement isdetected, suggesting landing and taxiing (region 327). 30 minutes afterthe wheels stop moving, an eleventh set of readings are taken (time 311)with the aircraft stationary on the ground (region 328).

Whilst the present invention has been described and illustrated withreference to particular embodiments, it will be appreciated by those ofordinary skill in the art that the invention lends itself to manydifferent variations not specifically illustrated herein. By way ofexample only, certain possible variations will now be described.

In certain embodiments, the control unit may store only a normalisedpressure reading that adjusts the measured pressure in view of themeasured temperature to yield a value of the expected pressure at acommon reference temperature. Such a temperature-normalised pressurereading, allows a comparison between pressure readings taken atdifferent temperatures. The control unit may also adjust pressurereadings to take into account whether the aircraft is on the ground withthe weight on the wheels, or in flight. When the aircraft is in the air,the pressure in the unloaded tires reduces by about 4%. If all such datais recorded by the control unit and then transmitted (uploaded) to adifferent device then such normalisation can be performed by means ofprocessing the data later. Such processing of the data can includeprocessing the data from multiple sensors together.

Embodiments of the invention have benefit in respect of aircraft thatare provided with an integrated tire pressure indicating system. Forexample, such embodiments allow maintenance crew to ascertain detailedtire pressure data quickly and easily and without needing to enter theaircraft.

Where in the foregoing description, integers or elements are mentionedwhich have known, obvious or foreseeable equivalents, then suchequivalents are herein incorporated as if individually set forth.Reference should be made to the claims for determining the true scope ofthe present invention, which should be construed so as to encompass anysuch equivalents. It will also be appreciated by the reader thatintegers or features of the invention that are described as preferable,advantageous, convenient or the like are optional and do not limit thescope of the independent claims. Moreover, it is to be understood thatsuch optional integers or features, whilst of possible benefit in someembodiments of the invention, may not be desirable, and may therefore beabsent, in other embodiments.

While at least one exemplary embodiment of the present invention(s) isdisclosed herein, it should be understood that modifications,substitutions and alternatives may be apparent to one of ordinary skillin the art and can be made without departing from the scope of thisdisclosure. This disclosure is intended to cover any adaptations orvariations of the exemplary embodiment(s). In addition, in thisdisclosure, the terms “comprise” or “comprising” do not exclude otherelements or steps, the terms “a” or “one” do not exclude a pluralnumber, and the term “or” means either or both. Furthermore,characteristics or steps which have been described may also be used incombination with other characteristics or steps and in any order unlessthe disclosure or context suggests otherwise. This disclosure herebyincorporates by reference the complete disclosure of any patent orapplication from which it claims benefit or priority.

The invention is:
 1. A tire pressure sensor device for a wheel of anaircraft, wherein the tire pressure sensor device comprises: a housing,a pressure sensor configured to measure an internal pressure of a tire,a temperature sensor configured to measure a temperature local to thetire, a memory unit local to the tire configured to store data, and acontrol unit local to the tire arranged to record in the memory unitdata in respect of multiple readings over time, wherein the housingaccommodates at least the control unit and the memory unit, and the dataso recorded for each such reading includes an indication of a time ofthe reading, an actual pressure as measured by the pressure sensor, anda temperature as measured by the temperature sensor, and the memory unitincludes an indication of a reference tire pressure for the tire, thememory unit configured to be read by a handheld device arranged tocompare the reference pressure with the actual pressure and to indicatewhether the actual pressure is suggestive that the tire is, or soon willbe, underinflated.
 2. The tire pressure sensor device according to claim1 further including a communication module facilitating secure wirelesscommunication with the handheld device.
 3. The tire pressure sensordevice according to claim 1, wherein the tire pressure sensor deviceincludes a motion sensor and wherein the control unit is configured todetect with the use of the motion sensor at least one of (a) whether theaircraft is in flight, and (b) whether the aircraft is on the ground. 4.The tire pressure sensor device according to claim 1 arranged such thatthe control unit records in memory both data relating to a reading takenwhen the aircraft is on the ground and data relating to a reading takenwhen the aircraft is in flight.
 5. The tire pressure sensor deviceaccording to claim 4 arranged such that the data so recorded for eachsuch reading includes an indication of whether the aircraft is on theground or an indication of whether the aircraft is in flight.
 6. Thetire pressure sensor device according claim 1, wherein the housingaccommodates: at least a part of the pressure sensor, at least a part ofthe temperature sensor, and a local source of electric power.
 7. Thetire pressure sensor device according to claim 1, wherein the controlunit is arranged to record the data when the wheel is not spinning 8.The tire pressure sensor device according to claim 7, wherein thecontrol unit is arranged to record the data a pre-determined time periodafter which the wheel has stopped spinning.
 9. The tire pressure sensordevice according to claim 1, wherein the control unit is arranged torecord the data in respect of multiple readings over time.
 10. The tirepressure sensor device according to claim 9 wherein the multiplereadings include a reading taken while the aircraft is on the ground,and another reading taken while the aircraft is in flight.
 11. A systemfor monitoring aircraft tire pressures, the system comprising: a tirepressure sensor device for a wheel of an aircraft, wherein the tirepressure sensor device comprises: a housing, a pressure sensorconfigured to measure an internal pressure of a tire, a temperaturesensor configured to measure a temperature local to the tire, a memoryunit local to the tire configured to store data, a control unit local tothe tire arranged to record in the memory unit data in respect ofmultiple readings over time, and a communications module configured forwireless communication; wherein the housing accommodates at least thecontrol unit and the memory unit, and the data so recorded for each suchreading includes an indication of a time of the reading, an actualpressure as measured by the pressure sensor, and a temperature asmeasured by the temperature sensor, and the memory unit includes anindication of a reference tire pressure for the tire; and a handhelddevice configured for wireless communication with the tire pressuresensors to download data from the memory unit, to compare the referencepressure with the actual pressure and to indicate whether the actualpressure is suggestive that the tire is, or soon will be, underinflated.12. The system of claim 11, comprising a plurality of tire pressuresensor devices, wherein the handheld device is configured to downloaddata from the memory unit of each sensor substantially at the same time.13. The system of claim 11, wherein wireless communication between thetire pressure sensor device and the handheld device is encrypted.
 14. Amethod of monitoring the pressure of a tire on an aircraft comprising: acontrol unit causing a measurement to be taken of actual tire pressureand of an associated temperature local to the tire, the control unitrecording, in a memory unit, data including an indication of the time atwhich the measurement is taken, an indication of the actual tirepressure and an indication of the associated temperature, the controlunit recording, in the memory unit, an indication of a reference tirepressure for the tire, reading, using a handheld device external to thetire pressure sensor device, the data including the indication of thetime at which the measurement is taken, the indication of the actualtire pressure and the indication of the temperature, and the indicationof the reference tire pressure, comparing, using the handheld device,the reference pressure with the actual pressure, and indicating whetherthe actual pressure is suggestive that the tire is, or soon will be,underinflated.
 15. The method according to claim 14, wherein the methodcomprises the control unit causing multiple measurements to be taken, atleast one measurement taken when the aircraft is on the ground, and atleast one further measurement taken when the aircraft is in flight. 16.The method according to claim 14, wherein the method comprises thecontrol unit recording the data when a wheel to which the tire isattached is not spinning.
 17. The method according to claim 16, whereinthe method comprises the control unit recording the data apre-determined time period after which the wheel has stopped spinning.18. The method according to claim 14, wherein the control unit ismounted to a wheel which includes the tire.